The desire to integrate data, voice, image and video over high speed digital trunks has led to the development of a variety of packet switching techniques. One such technique is called frame relay. A frame relay network provides a user with multiple independent data links to one or more destinations. User traffic on these data links is statistically multiplexed to provide efficient use of access lines and network resources. Since the multiplexing is at the link layer, end-to-end delay is minimized. Frame relay networks transfer user traffic without regard to content, thereby providing service which is effectively as transparent as a leased line. A frame relay network typically consists of a number of interconnected nodes which are capable of receiving data from other network nodes and forwarding that data through to other network nodes to its ultimate destination. Nodes are interconnected by transmission paths, each of which supports one or more virtual circuits. Communication from one user to another can thus be made using the pre-defined network connections of the virtual circuits.
Asynchronous Transfer Mode (ATM) is a second packet switching technology that provides users with the ability to connect to one or more users in a transparent fashion. Unlike the variable length packets used by frame relay services, ATM service is based on switching fixed length packets of data known as cells. Cell switching, as it is called, is gaining popularity for a variety of reasons. First, switch architectures can be optimized to switch cells at much higher speeds than variable length packets. Second, multiple services requiring a variety of quality of service guarantees can be provided simultaneously. ATM user traffic must be segmented into cells, transmitted, then reassembled back into its original form. This segmentation and reassembly (SAR) process is done in a standardized way, regardless of the carrier providing the ATM service.
Although the use of variable length packets in frame relay can be more efficient in terms of overhead and bandwidth used when compared with the fixed length cells used in ATM, other problems, such as delay and latency, present themselves. In frame based environments, passing traffic from one end to another is somewhat unpredictable by nature. For example, if one virtual circuit is using a significant amount of bandwidth, it will have a tendency to choke out other sources. Also, if one virtual circuit is transporting relatively large frames through the network, other circuits with smaller frames may suffer. This is known as latency. For example, it is not uncommon for two sources, one transmitting large frames and the other transmitting smaller frames to be transported over the same wire. As the larger frame is being transported over the wire, the smaller frame will have to wait a relatively long period of time before it is transmitted on the wire. If both sources are transmitting latency insensitive traffic, e.g., data, this may not be a problem. However, if the smaller frame source is transmitting multimedia traffic (e.g., especially voice) which is very time sensitive, this latency can seriously degrade the quality of the service provided by the network. The latency problem is compounded if the wire is a relatively slow link.
One solution to the problems of latency and delay has been to fragment large frames into smaller packets for transmission through a frame relay network. Unfortunately, no standardized method of frame relay fragmentation has been adopted. As a result, a number of non-standard fragmentation schemes have been used. These non-standard fragmentation schemes lead to interoperability problems, generally resulting in increased user costs. In addition, for those users who do not have access to frame relay networks that use frame fragmentation schemes, the problems of latency and delay remain.